Cardiac Transplantation in the Rat

Cardiac transplantation between inbred rat strains that differ for weak histocompatibility antigens is associated with the development of arteriosclerosis in the arteries of the donor graft myocardium. The lesions are seen in donor/recipient pairs that differ for both MHC and non-MHC histocompatibility antigens that apparently stimulate a low-level, chronic rejection of the donor heart graft. The arteriosclerosis associated with this chronic rejection consists of a diffuse, concentric proliferation of the intima and pathologically resembles the lesions observed in the coronary arteries of long-term human cardiac graft recipients. We have recently examined the influence of positive and negative manipulation of the host immune response on the development of the graft arteriosclerosis. Our results demonstrate that delayed harvest of the cardiac grafts or immunization with donor skin grafts or splenic lymphocytes increases the sensitivity of the recipient to the donor heart grafts--and, under conditions that allow for the long-term survival of the graft--increases the severity of the arteriosclerotic lesions. Alternatively, suppression of the host immune responses with cyclosporine or FK506, substantially reduces the arteriosclerotic changes. These results suggest that control of accelerated graft arteriosclerosis in long-term human cardiac recipient may require more careful and effective immunosuppression of the allograft reaction.